Recently, magnetic materials that utilize the direction of magnetization as a memory bit of information have been increasingly expected to be applied to high-performance non-volatile memories. In particular, a technique for electrically controlling the magnetization in a magnetic body using a phenomenon called spin torque (spin injection magnetization reversal) is being developed (Non Patent Literature 1, 2). By using the spin torque, magnetization state of a giant magnetoresistance element, a tunneling magnetoresistance element, or a ferromagnetic thin wire can be controlled by electric current and/or field.
In addition, nowadays, a magnetization control mechanism by current-induced effective magnetic field using an ultrathin magnetic layer has been reported, and the establishment of a magnetization control method with further lower electric power is expected (Non Patent Literature 3). The current-induced effective magnetic field is thought to be due to a phenomenon that occurs by using different materials on both interfaces of a magnetic layer and reducing the thickness of the magnetic layer (Rashba effect or the like) or a spin hall effect in a non-magnetic layer adjacent to the magnetic layer.
A CoFeB perpendicularly magnetized film in which a CoFeB transition metal alloy is used as a magnetic layer, one layer in contact with the magnetic layer is an oxide layer made of MgO or the like, and the other layer in contact is a seed layer made of Ta or the like is a structure used in a tunneling magnetoresistance element (Non Patent Literature 4) and also is a system in which a current-induced effective magnetic field is generated (Non Patent Literature 5). It is known so far that magnetization of the magnetic layer can be controlled with low current using the current-induced effective magnetic field.
In order to effectively utilize spin injection magnetization reversal and the current-induced effective magnetic field, a thinner film thickness of the magnetic layer is better. According to an earlier study however, it is found that, when the film thickness of a magnetic layer made of CoFeB or the like is set at 1.5 nm or less, in particular 1 nm or less, the magnetization and the magnetic anisotropy decrease, and thus such a layer cannot be used as a magnetic layer.